1. Field of the Invention
The present invention relates to a power supply for an inverter, which is connected at the output end to an electric power supply network via a throttle. The present invention also relates to a method for operating such a power supply.
2. Discussion of Background Information
Electric inverters require a power supply for operation, for generating a supply voltage for the regulating and control units of the inverter as well as the electronic components installed in the inverter. This supply voltage is often made available by a switched-mode power supply which may also be integrated into the inverter. Such inverters are also used for, among other things, connecting an energy source, for example, a photovoltaic system, a wind power plant, an electric power storage mechanism, a fuel cell, etc., to an electric supply network in order to feed generated electric power into the supply network. At the output end of the supply network, such inverters often have filter units such as a throttle, for example. The switched-mode power supply acquires the electric power needed for operation from the electric supply network, in particular to then be able to operate and/or service the inverter, in particular when the electric power storage mechanism cannot supply any electric power, for example, at night in the case of a photovoltaic system or in the absence of wind in the case of a wind power plant. Conversely, in the event of a failure of the electric supply network due to a short circuit in the supply network, for example, the switched-mode power supply and thus also the inverter would also fail. The electric power source could then no longer supply electric power to the supply network. However, various standards stipulate that an inverter must remain in operation for a certain period of time in the event of a failure of the electric power system in order to be able to support the power supply network by supplying the active power on demand. Therefore, measures are necessary so that, even when the electric supply network fails, it is possible to continue operation of the inverter, which is operated by a switched-mode power supply that receives its power supply from the electric supply network.
Capacitors are frequently used for this purpose in the switched-mode power supply in order to buffer the voltage supply for the required period of time. The disadvantage of this approach is that such a capacitor buffer can be designed only for a certain precisely defined period of time and also requires an enormous amount of space in the inverter and/or in the switched-mode power supply because of the large capacitors required. Furthermore, the expensive capacitors and other electric components also necessitate high costs.
As a possible alternative, it is also known that a second power supply network part, which obtains its energy from the electric power storage mechanism in the event of a system failure, can be provided in the switched-mode power supply. However, this approach is also associated with a substantial requirement for space and high costs in order to be implementable. Such a power supply is known from DE 10 2008 032 317 A1, for example. The power supply of DE 10 2008 032 317 A1 has a transformer with two primary windings of two primary circuits, where a first primary circuit receives power from the intermediate circuit of the converter and the second primary circuit receives power from the power supply network, switching back and forth between the two primary circuits, depending on the voltage applied in the second primary circuit. Each primary circuit comprises a PWM switch with the respective PWM controller.